1. Field of the Invention.
This invention is in the field of synchronous central processors of large-scale, high-performance, general-purpose digital data processing systems. More particularly, this invention relates to a distributor for the central execution pipeline unit of a central processor, which distributor serves as a communications center by which machine words are transmitted between units of the central processor and which has the capability of aligning machine words as required.
2. Description of the Prior Art.
To increase the performance of the central processors (CPU's) of data processing systems of which they are a part, many modifications and improvements have been incorporated into such CPU's. One such modification is the use of a high-speed cache unit located in the CPU to minimize the time required to fetch operands and instructions. To further increase the performance of CPU's, they are synchronized; i.e., a clock produces a clock pulses which control each step, or stage, of the operation of the CPU. Synchronization permits paralleling, overlapping, or pipelining the execution of instructions by dividing the process of executing each instruction into a number of sequential steps, with each instruction going through the same sequence of steps one after another.
In a CPU having several execution units, with each execution unit being capable of executing a subset of the instruction repertoire of the CPU and which execution units operate substantially independently of each other, it is desirable that the central execution pipeline unit of the CPU initiate the execution of instructions, including the fetching of the operand, or target word, or operands, of each instruction, in a series of steps or stages, each requiring one clock period to complete, and through which each instruction progresses so that, at the completion of the last stage of the central execution pipeline, an instruction and its operands, or target words, are available and ready for execution, or the instruction is executed by the appropriate execution unit.
In order to make the target words of an instruction available and ready for execution by one of the plurality of execution units as each instruction completes its passage through the central execution pipeline unit, there is a requirement that the target words, from whatever the source, and there are more than one, be transmitted to the execution units as expeditiously as possible. Since certain operations, or instructions, require the data in the target word or words to be aligned, alignment of the target word should be accomplished prior to its receipt by the execution unit to which it is addressed. Such a CPU also needs a means for transmitting information between units of the CPU, in addition to the execution units and within the central pipeline execution unit itself, as expeditiously as possible to maximize the performance of the CPU.